Nonsyndromic cleft lip with or without cleft palate (NSCLP) is one of the five most common birth defects affecting 4,000 newborns per year in the United States. The etiology of NSCLP is complex. Although a number of susceptibility loci have been identified, they are postulated to play only a small etiologic role. The challenge now is to identify the genes that play a major role. [unreadable] [unreadable] A recent study in the mouse suggests that there are major NSCLP loci and that they can be identified. To accomplish this task, it is important to have a defined population and the methodology to detect linkage with and without association. Towards these goals, we have identified and characterized a large sample of multiplex NSCLP families. This unique resource of NSCLP families provides strong evidence that genetic factor(s) play an important role. Using these families, we have positionally identified four new candidate chromosomal regions and confirmed six chromosomal regions from a recent sib-pair analysis study that may contain NSCLP loci. [unreadable] [unreadable] In this continuing work, we will use our unique and large set of multiplex NSCLP families to refine these new candidate regions and test a set of biologically relevant candidate genes. At the same time, we will expand our multiplex families and then conduct a dense 5 cM genome-wide scan to optimize detection of NSCLP genetic loci. Parametric and nonparametric analyzes will incorporate environmental and vitamin exposures and maternal genotype information. Finally all candidate NSCLP genes yielding positive results will be tested in ethnically diverse simplex trios that we are collecting. The results of this study will provide insights into the causes of familial NSCLP and may yield new information about isolated NSCLP. Finally, identification of high-risk genotypes may lead to the development of prevention programs in selected populations and may suggest gene-based prevention strategies. [unreadable] [unreadable]